308 
Psyche 
[December 
nymph, lacking the last few abdominal segments (Plate 28). It is 
apparently douglassi but the specimen is much smaller than the type 
of douglassi and presumably represents a much younger stage, the 
wing pads being relatively small. In the type of douglassi the length 
of the wing pads was three times the width of the thorax; in the 
Herdina. specimen the wing pads (7 mm. long) are only about equal 
to the width of the thorax. Since the wing pads are in the same 
position in both nymphs, it is clear that they were independent in 
the early stages as well as in the more advanced ones. The other 
megasecopterous nymph (No. HTP 43) is in the collection of Helen 
and Ted Piecko. This is a very fine specimen, lacking only the end 
of the abdomen. It is about the same size as the type of douglassi , 
the fore wing being 15 mm. long, which is about three times the 
width of the thorax. The wings are in the same position as they are 
in the other mischopterid nymphs. This specimen is almost certainly 
douglassi but many structural details remain to be excavated before 
the identification is certain. At any rate it is clear from these nymphs 
that the oblique-lateral position of the wing pads is the normal one 
in this family of Megasecoptera and that the position is constant dur- 
ing the various stages of growth rather than acquired by the older 
nymphs. 
Discussion 
The type of douglassi and the other specimens mentioned above 
make a major contribution to our understanding of nymphal develop- 
ment of the Megasecoptera. First, it is now clear that the Megasecop- 
tera were exopterygote insects, not endopterygotes, as Lameere, Forbes 
and others have believed. Second , the oblique-lateral position of the 
wing pads strongly suggests that the wings in the primitive paleop- 
terous insects developed in that way. 5 This is supported by the 
discovery of Permian mayfly nymphs (from Moravia and Oklahoma) 
in which the wing pads are independent and oblique in all stages 
(Personal communication, J. Kukalova; see her article in this issue 
of Psyche). According to this view, the position of the wing pads 
in the Ephemeroptera. and Odonata, fixed longitudinally over the 
thorax and abdomen, is a secondary one, possibly an adaptation to the 
Additional evidence is given by the very recent discovery of a whole 
nymph unquestionably belonging to the Palaeodictyoptera. This fossil was 
found after the present paper was written, in the course of our search for 
additional megasecopterous nymphs. The palaeodictyopterous nymph, which 
has the wings positioned as in the mischopterids, will be described in a 
later paper. 
